Transformation Of Waves Over Three-Dimensional Reef

The reefs are the important part of the marine environment.With the enhancement of Chinese maritime rights consciousness,the development and utilization of reefs become an indispensable part of national development.In recent years,many countries have begun to build port structures on the reefs.And,the waves as the main load of the marine buildings and ships become a key factor in the development of the reefs.When waves propagate from deep water to shallow water near the reef,they will experience larger nonlinear transformation,such as the wave crest became sharp and the trough became flat,the whole wave forward or backward.All these transformations are affected by the change incline water depth.And these transformations are mainly expressed by the nonlinear characteristic of waves,that is,the asymmetry,the skewness,the kurtosis and the Ursell number.In this paper,a physical model test is carried out on the transformation of the waves on the reef.The layout,test conditions and experimental contents of the reef test are introduced in detail.Then,the non-hydrostatic model SWASH is used to study the reef test.The numerical simulation data are consistent with the physical model test data.The article then analyzes the data obtained from the reef test.By comparing the changes of the wave surface and the wave spectrum,it can be seen that both the wave surface and the wave spectrum had large transformations when waves travel from deep water to shallow water.The wave height distribution and wave set-up and set-down are also changed.In the deep water area,wave height distribution follows the Rayleigh distribution.As the deep of the water shoals,the wave height distribution gradually deviates from the Rayleigh distribution and tends to follow Glukhovskiy distribution.Wave set-up and set-down are closely related to the wave height,the wave period and the moving depth of water.In this paper,we analyzeds the impacts of these factors on wave set-up and set-down.Then,the article analyzes the changes of nonlinear characteristics of waves in the transformation of waves over the reef.We focus on the changes of nonlinear characteristic parameters of waves.There are two cases of irregular waves in this paper,one is the wind waves,and the other is the mixed waves of wind wave and swell.Based on wind waves,we consider the influence of the significant wave height,wave period,wave direction and spectrum bandwidth on the wave non-linearity.The results show that the Ursell number and the asymmetry are more affected by the significant wave height and the wave period.The larger the significant wave height and the wave period of waves,the greater the value of the Ursell number and the asymmetry(absolute value)in shallow water.And the growth of Ursell number in the shallow water is also affected by the spectrum bandwidth,its value increases with the increase of spectrum bandwidth.The significant wave height,wave period,wave direction and spectrum bandwidth have little effect on the value of the skewness and the kurtosis.Then,we consider the effect of significant wave height and wave direction on the mixed waves of wind waves and swell.In this paper,we also compare the mixed waves with the wind waves to analysis the differences of wave nonlinear characteristic parameters in different wave conditions.As the result,the Ursell number and the asymmetry of mixed waves are only affected by the significant wave height,and have little affected by wave direction.The skewness and the kurtosis are not affected by the significant wave height and wave direction.Comparing with the wind waves,the Ursell number and the asymmetry of the mixed waves are larger in the shallow water,but,the changes of the skewness and the kurtosis is basically the same.At last,the article analyzes the variation of wave nonlinearity based on the idea of wavelet transformation.We focus on the nonlinear characteristics of the irregular waves.The analysis shows that the wave-wave interaction was enhanced in shallow water,and increasing wave components participated in this interaction.With the waves broking,the high-order harmonics are released as free waves,so that the degree of nonlinear interaction of waves is reduced.And if the free waves are re-involved in the nonlinear interaction of the waves,the range of the wave-wave interaction is increased.If the free waves are not involved in the wave-wave interaction,the range of the wave nonlinear interaction decreased with its degree.